ADB Device not found in shell

I am trying to install CWM for my rk2928 device,

Here is how I done ;

adb devices

List of device attached 8AC7QGZ8GA device

adb shell

shell@android:/ $ adb push flash_image /dev/ error: device not found ?

ScreenShot [here](http://ift.tt/1D1Z1RB"ADB ScreenShot")

All the drivers are installed properly What I do ?